Driving circuit for voice coil motor

ABSTRACT

With a driving current as I DRV , with a reference voltage as V REF , and with a gain as k, a current detection circuit generates a detection voltage V S  represented by V S =V REF +k×I DRV . An error amplifier amplifies a difference between the detection voltage V S  and a control voltage that indicates a position of the VCM so as to generate an error voltage V ERR . A first driver switches the driving current I DRV  between a source current and a sink current with respect to one end of the coil according to the error voltage V ERR . A second driver switches the driving current I DRV  between a sink current and a source current with respect to the other end of the coil according to the error voltage V ERR . The driving circuit allows an external circuit to set the level of the reference voltage V REF .

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation under 35 U.S.C. §120 ofPCT/JP2014/002340, filed Apr. 25, 2014, which is incorporated hereinreference and which claimed priority to Japanese Application No.2013-094521, filed Apr. 26, 2013. The present application likewiseclaims priority under 35 U.S.C. §119 to Japanese Application No.2013-094521, filed Apr. 26, 2013, the entire content of which is alsoincorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a control technique for a voice coilmotor.

2. Description of the Related Art

Digital still cameras, digital video cameras, or electronic devices(e.g., cellular phones) having an image acquisition function include anactuator for positioning a focusing lens. Known examples of suchactuators include actuators using a stepping motor method, actuatorsusing a piezoelectric method, and actuators using a voice coil motor(VCM) method.

A VCM is capable of generating driving power in a linear direction thatcorresponds to the direction of a current that flows through its coil.Known examples of such a VCM driving method include a spring returnmethod and a bi-directional driving method.

With a spring return mechanism VCM, a driving current is supplied to acoil so as to generate a driving force in a first direction.Furthermore, a driving force is generated in a second direction that isthe opposite of the first direction by means of a spring coupled with amoving element. That is to say, the spring return mechanism VCM isconfigured as a combination of an electrical driving mechanism and adynamic driving mechanism. In a case of employing such a spring returnmechanism VCM as a driving source, such an arrangement requires only adriving current that flows through the coil in a single direction,thereby allowing the driving circuit to have a simple configuration.

In contrast, in the bi-directional driving method, such an arrangementemploys a driving circuit such as an H-bridge circuit that is capable ofswitching the driving current between a source current and a sinkcurrent on respective ends of the VCM. With the bi-directional drivingmethod, such an arrangement is capable of switching the direction of thecoil current, thereby allowing the driving force to be provided in boththe positive direction and the negative direction.

With the spring return method, the VCM requires no driving currentsupply when the position of the VCM is zero (reference position). Incontrast, with the bi-directional driving method, the driving currentfor the VCM can be set to substantially zero even if the referenceposition is set to a desired value. Thus, such an arrangement has anadvantage from the viewpoint of low power consumption.

A driving circuit according to a conventional bi-directional drivingmethod is configured to have left-right symmetry. With the direction ofa current that flows through the coil of the VCM in the first directionas a positive direction, the driving circuit is configured to generate adriving current in a range between −I_(MAX) and I_(MAX) with a currentvalue of zero as the center.

However, in some cases, there is a difference in the optimum drivingcurrent range between manufacturers of VCMs to be driven, between modelsof VCMs, or otherwise between sets mounting such VCMs.

SUMMARY OF THE INVENTION

The present invention has been made in order to solve such a problem.Accordingly, it is an exemplary purpose of an embodiment of the presentinvention to provide a VCM driving circuit which is capable of settingthe current range.

An embodiment of the present invention relates to a driving circuit thatsupplies a bi-directional driving current to a voice coil motor. Thedriving circuit comprises: a current detection circuit that generates adetection voltage V_(S) represented by V_(S)=V_(REF)+k×I_(DRV), with thedriving current as I_(DRV), with a reference voltage as V_(REF), andwith a gain as k; an error amplifier that amplifies a difference betweenthe detection voltage V_(S) and a control voltage that indicates aposition of the voice coil motor so as to generate an error voltage; afirst driver that is connected to one end of a coil of the voice coilmotor, and that switches the driving current between a state in whichthe driving current flows as a source current and a state in which thedriving current flows as a sink current according to the error voltage;and a second driver that is connected to the other end of the coil ofthe voice coil motor, and that switches the driving current between astate in which the driving current flows as a sink current and a statein which the driving current flows as a source current according to theerror voltage. The driving circuit is configured to be capable ofsetting the level of the reference voltage V_(REF) externally.

With such an embodiment, the relative relation between the controlvoltage and the driving current I_(DRV) can be shifted according to thereference voltage V_(REF). Thus, such an arrangement is capable offreely setting the range of the driving current.

Also, the current detection circuit may comprise: a detection resistorarranged on a path of the driving current; a first operationalamplifier; a first resistor arranged between a first input terminal ofthe first operational amplifier and a first end of the detectionresistor; a second resistor arranged between a second input terminal ofthe first operational amplifier and a second end of the detectionresistor; a third resistor arranged between an output terminal of thefirst operational amplifier and the first input terminal of the firstoperational amplifier; and a fourth resistor having one end connected tothe second input terminal of the first operational amplifier and anotherend to which the reference voltage is applied.

Also, the driving circuit according to an embodiment may furthercomprise: a first D/A converter that converts, into the control voltageconfigured as an analog signal, digital control data that is receivedfrom an external processor and that indicates the position; and a secondD/A converter that converts, into the reference voltage configured as ananalog signal, correction data that is received from the externalprocessor and that indicates the reference voltage.

Such an arrangement is capable of freely setting, according to the valueof the correction data, the range of the driving current to be generatedaccording to the range of the digital control data.

Also, the detection resistor may be arranged between the first end ofthe coil and an output terminal of the first driver, or otherwisebetween the second end of the coil and an output terminal of the seconddriver.

Also, the on resistance of a transistor that forms an output stage ofthe first driver and the on resistance of a transistor that forms anoutput stage of the second driver may be used as the detection resistor.

Also, a known DC resistance component of the voice coil motor may beused as the detection resistor.

Also, the error amplifier may comprise: a second operational amplifierhaving a first input terminal to which the control voltage is input; afirst capacitor arranged between a second input terminal and an outputterminal of the second operational amplifier; and a fifth resistorhaving a first end connected to the second input terminal of the secondoperational amplifier and a second end to which the detection voltage isapplied.

Also, the first driver may comprise a non-inverting amplifier thatamplifies the error voltage with a predetermined common voltage as areference voltage so as to apply a first driving voltage to the firstend of the coil. Also, the second driver may comprise an invertingamplifier that amplifies the error voltage with the common voltage as areference voltage so as to apply a second driving voltage to the secondend of the coil.

Also, the first driver may comprise: a first voltage-dividing circuitthat divides, with a predetermined voltage division ratio, a voltagedifference between a first output voltage that develops at the first endof the coil and a predetermined common voltage; and a first amplifierthat comprises a first push-pull output stage including a high-sidetransistor and a low-side transistor, and that controls the high-sidetransistor and the low-side transistor of the push-pull output stagesuch that the voltage obtained by voltage division by means of the firstvoltage-dividing circuit approaches to the error voltage. Aldo, thesecond driver may comprise: a second voltage-dividing circuit thatdivides, with a predetermined voltage division ratio, a voltagedifference between a second output voltage that develops at the secondend of the coil and the error voltage; and a second amplifier thatcomprises a second push-pull output stage including a high-sidetransistor and a low-side transistor, and that controls the high-sidetransistor and the low-side transistor of the push-pull output stagesuch that the voltage obtained by voltage division by means of thesecond voltage-dividing circuit approaches to the common voltage.

Another embodiment of the present invention also relates to a drivingcircuit that supplies a bi-directional driving current to a voice coilmotor. The driving circuit comprises: a current detection circuit thatgenerates a detection voltage V_(S) that corresponds to the drivingcurrent; an error amplifier that amplifies a difference between thedetection voltage and a control voltage that indicates a position of thevoice coil motor so as to generate an error voltage; a first driver thatis connected to one end of a coil of the voice coil motor, and thatswitches the driving current between a state in which the drivingcurrent flows as a source current and a state in which the drivingcurrent flows as a sink current according to the error voltage; and asecond driver that is connected to the other end of the coil of thevoice coil motor, and that switches the driving current between a statein which the driving current flows as a sink current and a state inwhich the driving current flows as a source current according to theerror voltage. The driving circuit is capable of superimposing a shiftvoltage that is settable by means of an external circuit on at least oneof the control voltage and the detection voltage. The error amplifiergenerates the error voltage such that the control voltage approaches tothe detection voltage after the shift voltage is superimposed on atleast one of the control voltage and the detection voltage.

With such an embodiment, the relative relation between the controlvoltage and the driving current I_(DRV) can be shifted according to theshift voltage. Thus, such an arrangement is capable of freely settingthe range of the driving current.

Also, the current detection circuit may generate a detection voltageV_(S) represented by V_(S)=V_(REF)+k×I_(DRV), with the driving currentas I_(DRV), with a reference voltage as V_(REF), and with a gain as k.Also, the level of the reference voltage V_(REF) may be settableaccording to correction data received from an external processor. Thisallows the shift voltage superimposed on the detection voltage to beadjustable according to the correction data.

Also, the control voltage may be obtained by adding a shift voltage thatcorresponds to correction data received from an external processor to avoltage that corresponds to digital control data that indicates aposition of the voice coil motor received from the external processor.

Such an arrangement is capable of controlling a shift voltagesuperimposed on the detection voltage according to the correction data.

Also, the control voltage may be obtained as a voltage by addingcorrection data received from an external processor to, or otherwise bysubtracting the aforementioned correction data from, digital controldata that indicates a position of the voice coil motor received from theexternal processor, and by converting the digital value thus obtainedinto an analog voltage.

Such an arrangement is capable of superimposing a shift voltage thatcorresponds to the correction data on the control voltage.

Also, the driving circuit may further comprise an adder that is arrangedas an upstream stage of the error amplifier, and that adds a shiftvoltage that corresponds to correction data received from an externalprocessor to, or otherwise subtracts the aforementioned correction datafrom, the detection voltage.

Such an arrangement is capable of superimposing a shift voltage thatcorresponds to the correction data on the control voltage.

Also, an offset voltage of the error amplifier may be adjustableaccording to correction data received from an external processor.

Also, the driving circuit may be monolithically integrated on a singlesemiconductor substrate.

Examples of such a “monolithically integrated” arrangement include: anarrangement in which all the circuit components are formed on asemiconductor substrate; and an arrangement in which principal circuitcomponents are monolithically integrated. Also, a part of the circuitcomponents such as resistors and capacitors may be arranged in the formof components external to such a semiconductor substrate in order toadjust the circuit constants.

Yet another embodiment of the present invention relates to a lensmodule. The lens module comprises: a focusing lens; a voice coil motorhaving a bi-directional mechanism or otherwise a spring return mechanismarranged such that a moving element thereof is coupled with the focusinglens; and the driving circuit according to any one of the aforementionedembodiments that drive the voice coil motor.

Yet another embodiment of the present invention also relates to a lensmodule. The lens module comprises: an image stabilization lens; a voicecoil motor having a bi-directional mechanism or otherwise a springreturn mechanism arranged such that a moving element thereof is coupledwith the image stabilization lens; and the driving circuit according toany one of the aforementioned embodiments that drive the voice coilmotor.

Yet another embodiment of the present invention relates to an electronicdevice. The electronic device comprises: any one of the aforementionedlens modules; and an image acquisition element that acquires an imagebased on light that has passed through the lens module.

It is to be noted that any arbitrary combination or rearrangement of theabove-described structural components and so forth is effective as andencompassed by the present embodiments.

Moreover, this summary of the invention does not necessarily describeall necessary features so that the invention may also be asub-combination of these described features.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments will now be described, by way of example only, withreference to the accompanying drawings which are meant to be exemplary,not limiting, and wherein like elements are numbered alike in severalFigures, in which:

FIG. 1 is a block diagram showing an overall configuration of anelectronic device according to an embodiment;

FIG. 2 is a block diagram showing a configuration of a lens moduleaccording to the embodiment;

FIGS. 3A through 3C are diagrams each showing the input/outputcharacteristics of a driving circuit shown in FIG. 2; and

FIG. 4 is a perspective view showing a cellular phone terminal which isan example of an electronic device.

DETAILED DESCRIPTION OF THE INVENTION

The invention will now be described based on preferred embodiments whichdo not intend to limit the scope of the present invention but exemplifythe invention. All of the features and the combinations thereofdescribed in the embodiment are not necessarily essential to theinvention.

In the present specification, the state represented by the phrase “themember A is connected to the member B” includes a state in which themember A is indirectly connected to the member B via another member thatdoes not substantially affect the electric connection therebetween, orthat does not damage the functions or effects of the connectiontherebetween, in addition to a state in which the member A is physicallyand directly connected to the member B. Similarly, the state representedby the phrase “the member C is provided between the member A and themember B” includes a state in which the member A is indirectly connectedto the member C, or the member B is indirectly connected to the member Cvia another member that does not substantially affect the electricconnection therebetween, or that does not damage the functions oreffects of the connection therebetween, in addition to a state in whichthe member A is directly connected to the member C, or the member B isdirectly connected to the member C.

FIG. 1 is a block diagram showing an overall configuration of anelectronic device 500 according to an embodiment. The electronic device500 is configured as a cellular phone having an image acquisitionfunction, a digital still camera, a video camera, a web camera, a tabletPC (Personal Computer), or the like. The electronic device 500 includesa lens module 502, an image acquisition element 504, an image processingprocessor 506, and a CPU (Central Processing Unit) 508.

The lens module 502 is provided in order to provide a so-calledautofocus function. The lens module 502 includes a focusing lens 512 andan actuator 510. The lens 512 is held such that it can be moved in theoptical axis direction. The actuator 510 controls the position of thelens 512 according to an instruction value S1 received from the CPU 508.

Light (an image) is input to the image acquisition element 504 after ithas passed through the lens 512. The image processing processor 506reads out the image data from the image acquisition element 504.

The CPU 508 determines the target position to which the focusing lens512 is to be set, based on the image read out by the image processingprocessor 506, such that the image that has passed through the focusinglens 512 forms an image on the image acquisition element 504.Furthermore, the CPU 508 outputs an instruction value S1 to the actuator510 according to the target position thus determined.

The above is the overall configuration of the electronic device 500.Next, description will be made regarding a specific configuration of thelens module 502.

FIG. 2 is a block diagram showing a configuration of the lens module 502according to the embodiment.

The lens module 502 includes a voice coil motor (VCM) 200 and a drivingcircuit 2.

The VCM 200 is configured as an actuator that provides positioning ofthe focusing lens (512 in FIG. 1). The VCM 200 is arranged such that itsmoving element is coupled with the focusing lens.

The driving circuit 2 includes output terminals OUT+ and OUT−, a powersupply terminal PVDD, a ground terminal PGND, and an interface terminalIF.

A power supply voltage V_(DD) is supplied to the power supply terminalPVDD. A ground voltage V_(GND) is supplied to the ground terminal PGND.The interface terminal IF is connected to the external CPU 508 via abus. The CPU 508 supplies, to the driving circuit 2, control dataD_(CNT) which indicates a stroke amount (target position, displacement)for the moving element of the VCM 200.

A coil L1 of the VCM 200 to be driven is connected between the outputterminals OUT+ and OUT−. The driving circuit 2 supplies a bi-directionaldriving current I_(DRV) to the coil L1 of the VCM 200 according to thecontrol data D_(CNT), so as to control the position of the movingelement. When the driving current I_(DRV) that flows through the coil L1is zero, the moving element comes to a stop at the predeterminedreference position. When the driving current I_(DRV) flows through thecoil L1 in the positive direction, the position of the moving element ischanged in the first direction according to the current value.Conversely, when the driving current I_(DRV) flows through the coil L1in the negative direction, the position of the moving element is changedin the second direction according to the current value. Description willbe made in the present embodiment with the direction in which thedriving current I_(DRV) flows from the output terminal OUT+ to theoutput terminal OUT− as the positive direction.

The driving circuit 2 includes a current detection circuit 10, an erroramplifier 20, a first driver 30, a second driver 40, a logic unit 50, afirst D/A converter 52, a second D/A converter 54, and a buffer 56.

The logic unit 50 includes an interface circuit that transmits andreceives data or instructions between it and the CPU 508, and a registeror the like that stores the data received from the CPU 508.

The current detection circuit 10 detects the driving current I_(DRV)that flows through the coil L1, and generates a detection voltage V_(S)that corresponds to the driving current I_(DRV). The detection voltageV_(S) is represented by the following Expression (2) using a gain k anda reference voltage V_(REF).

V _(S) =V _(REF) +k×I _(DRV)  (2)

For example, the current detection circuit 10 includes a detectionresistor R_(NF), a first resistor R1, a second resistor R2, a thirdresistor R3, and a fourth resistor R4.

The detection resistor R_(NF) is arranged on a path of the drivingcurrent I_(DRV). For example, the detection resistor R_(NF) is arrangedbetween the second end of the coil L1 and the output terminal of thesecond driver 40. Alternatively, the detection resistor R_(NF) may bearranged between the first end of the coil L1 and the output terminal ofthe first driver 30. A voltage drop V_(NF) occurs at the detectionresistor R_(FN) in proportion to the driving current I_(DRV).

The first resistor R1 is arranged between the first input terminal(inverting input terminal) of a first operational amplifier 12 and afirst end E1 of the detection resistor R_(NF). The second resistor R2 isarranged between the second input terminal (non-inverting inputterminal) of the first operational amplifier 12 and a second end E2 ofthe detection resistor R_(NF). The third resistor R3 is arranged betweenthe output terminal and the first input terminal (inverting inputterminal) of the first operational amplifier 12. The fourth resistor R4is arranged such that its one end is connected to the second inputterminal (non-inverting input terminal) of the first operationalamplifier 12 and such that the reference voltage V_(REF) is applied toits other end.

In the following description, V1 represents an electric potential at thefirst end E1 of the detection resistor R_(NF), and V2 represents anelectric potential at the second end E2 of the detection resistorR_(NF). When the relation (R1=R2=Ra) and the relation (R3=R4=Rb) holdtrue, the detection voltage V_(S) is represented by the followingExpression (3).

V _(S) =V _(REF) +Rb/Ra×(V2−V1)  (3)

By substituting Expression (3) into Expression (4), Expression (5) isobtained.

V _(NF) =V2−V1=R _(NF) ×I _(DRV)  (4)

V _(S) =V _(REF) +Rb/Ra×R _(NF) ×I _(DRV)  (5)

Thus, the gain k of the current detection circuit 10 is represented by(Rb/Ra×R_(NF)).

It should be noted that the configuration of the current detectioncircuit 10 is not restricted to such a configuration shown in FIG. 2.Also, the current detection circuit 10 may have other configurations.

The first D/A converter 52 converts the control data D_(CNT), which isreceived by the logic unit 50 from the CPU 508, into an analog controlvoltage V_(CNT). The control voltage V_(CNT) indicates a target strokeamount to be applied to the moving element of the VCM 200.

The driving circuit 2 according to the present embodiment is configuredto allow an external circuit to set the level of the reference voltageV_(REF). Specifically, the logic unit 50 is configured to receive, fromthe CPU 508, correction data D_(REF) that indicates the referencevoltage V_(REF). The second D/A converter 54 converts the correctiondata D_(REF) received by the logic unit 50 into the analog referencevoltage V_(REF).

The error amplifier 20 amplifies a difference between the controlvoltage V_(CNT) that indicates the position value for the voice coilmotor and the detection voltage V_(S) so as to generate an error voltageV_(ERR). For example, the error amplifier 20 may be configured as anintegrator. For example, the error amplifier 20 includes a secondoperational amplifier 22, a first capacitor C1, and a fifth resistor R5.

The control voltage V_(CNT) is input to the first input terminal(non-inverting input terminal) of the second operational amplifier 22.The first capacitor C1 is arranged between the second input terminal(inverting input terminal) and the output terminal of the secondoperational amplifier 22. The fifth resistor R5 is arranged such thatits first end is connected to the second input terminal (inverting inputterminal) of the second operational amplifier 22, and such that thedetection voltage V_(S) is applied to its second end.

It should be noted that the configuration of the error amplifier 20 isnot restricted to such an arrangement shown in FIG. 2.

The first driver 30 is connected to one end of the coil L1 of the voicecoil motor 200. The first driver 30 switches the driving current I_(DRV)according to the error voltage V_(ERR), between a state in which thedriving current I_(DRV) flows as a source current and a state in whichthe driving current I_(DRV) flows as a sink current.

The second driver 40 operates with the reverse phase of the first driver30. The second driver 40 is connected to the other end of the coil L1 ofthe voice coil motor 200. Furthermore, the second driver 40 switches thedriving current I_(DRV) according to the error voltage V_(ERR), betweena state in which the driving current I_(DRV) flows as a sink current anda state in which the driving current I_(DRV) flows as a source current.

The buffer 56 outputs a predetermined common voltage V_(COM). The firstdriver 30 includes a non-inverting amplifier that performs amplificationwithout inversion of the error voltage V_(ERR) with the common voltageV_(COM) as a reference voltage, and that applies a first driving voltageV_(O+) to the first end of the coil L1. In contrast, the second driver40 includes an inverting amplifier that performs amplification withinversion of the error voltage V_(ERR) with the common voltage V_(COM)as a reference voltage, and that applies, to the second end of the coilL1, a second driving voltage V_(O−) having the reverse phase of thefirst driving voltage V_(O+).

More specifically, the first driver 30 includes a first voltage-dividingcircuit 32 and a first amplifier 34. The first voltage-dividing circuit32 includes resistors R11 and R12, and divides the voltage differencebetween the first output voltage V_(O+) at the first end of the coil L1and the predetermined common voltage V_(COM) using a predeterminedvoltage division ratio. The first amplifier 34 includes a push-pulloutput stage comprising a high-side transistor MH and a low-sidetransistor ML. The first amplifier 34 controls the high-side transistorMH and the low-side transistor ML included in its push-pull output stagesuch that a voltage V_(FB+) obtained by the first voltage-dividingcircuit 32 approaches to the error voltage V_(ERR).

The second driver 40 includes a second voltage-dividing circuit 42 and asecond amplifier 44. The second amplifier 44 includes resistors R21 andR22, and divides the voltage difference between the second outputvoltage V_(O−) at the second end of the coil L1 and the error voltageV_(ERR) using a predetermined voltage division ratio. The secondamplifier 44 includes a push-pull output stage comprising a high-sidetransistor MH and a low-side transistor ML. The second amplifier 44controls the high-side transistor MH and the low-side transistor MLincluded in its push-pull output stage such that a voltage V_(FB−)obtained by the second voltage-dividing circuit 42 approaches to thecommon voltage V_(COM).

The above is the configuration of the driving circuit 2. Next,description will be made regarding the operation thereof. FIGS. 3Athrough 3C are diagrams each showing the input/output characteristics ofthe driving circuit 2 shown in FIG. 2.

Description will be made assuming that the control data D_(CNT) outputfrom the CPU 508 is configured as 10-bit data having a value rangingbetween 0x000(0) and 0x3FF (1023). As shown in FIG. 3A, when the codefor the control data D_(CNT) is 0x000 (0 in decimal notation), thecontrol voltage V_(CNT) is set to a lower reference voltage V_(L) (e.g.,0 V) provided by the first D/A converter 52. When the code for thecontrol data D_(CNT) is 0x3FF (1023 in decimal notation), the controlvoltage V_(CNT) is set to an upper reference voltage V_(H) provided bythe first D/A converter 52. In a case in which V_(L)=0 V, the controlvoltage V_(CNT) is represented by the following Expression with thecontrol data D_(CNT) in decimal notation as as X.

V _(CNT) =V _(H)×(X/1023)

The driving circuit 2 generates the driving voltages V_(O+) and V_(O−)by means of a feedback loop including the error amplifier 20 such thatthe detection voltage V_(S) matches the control voltage V_(CNT).

As described above, the detection voltage V_(S) is represented byExpression (3). Thus, the driving current I_(DRV) is feedback controlledso as to approach a target value represented by the followingExpression.

I _(DRV)=(V _(CNT) −V _(REF))/k.

The control voltage V_(CNT) is supplied in a voltage range between 0 andV_(H). Thus, the maximum value I_(MAX) of the driving current I_(DRV) isrepresented by I_(DRV)=(V_(H)−V_(REF))/k, and the minimum value I_(MIN)is represented by I_(DRV)=−V_(REF)/k. The width of the range of thedriving current I_(DRV), which is represented by ΔI=I_(MAX)−I_(MIN), isalso represented by V_(H)/k, which is a constant value regardless of thereference voltage V_(REF).

That is to say, with the driving circuit 2 shown in FIG. 2, the range ofthe driving current I_(DRV) can be freely set according to the level ofthe reference voltage V_(REF). For example, when the reference voltageV_(REF) is set to the center value V_(H)/2 of the voltage range of thecontrol voltage V_(CNT) ranging between 0 and V_(H), the relationI_(MAX)=−I_(MIN) holds true. In this case, the maximum value of thecurrent that can flow in the positive direction and the maximum value ofthe current that can flow in the negative direction are the same. Incontrast, when the reference voltage V_(REF) is set to a value that ishigher than the center value V_(H)/2, the current value that can flow inthe negative direction is greater than the current that can flow in thepositive direction. Conversely, when the reference voltage V_(REF) isset to a value that is lower than the center value V_(H)/2, the currentvalue that can flow in the positive direction is greater than thecurrent that can flow in the negative direction.

The driving circuit 2 is configured to be capable of setting thereference voltage V_(REF) to be supplied to the current detectioncircuit 10, according to the reference data D_(REF) received from theCPU 508 configured as an external component. The reference voltageV_(REF) is required to have only a low resolution as compared with thecontrol voltage V_(CNT). Accordingly, the number of bits of the secondD/A converter 54 may be on the order of 8 bits. In this case, thereference data D_(REF) is configured as 8-bit data.

With the reference data D_(REF) in decimal notation as Y, the referencevoltage V_(REF) is represented by the following Expression.

V _(REF) =V _(H) ×Y/255≈V _(H)×(4×Y)/1023

That is to say, when the control data D_(CNT) is equal to a valueobtained by multiplying the reference data D_(REF) by 4 (obtained by bitshifting the reference data D_(REF) by 2 bits toward the upper bitside), the driving current I_(DRV) becomes zero.

FIG. 3B shows the relation between the control voltage V_(CNT) and thedriving current I_(DRV) with the reference voltage V_(REF) as aparameter. FIG. 3C shows the relation between the control data D_(CNT)and the driving current I_(DRV) with the reference data D_(REF) thatindicates the reference voltage V_(REF) as a parameter.

The maximum value I_(MAX) and the minimum value I_(MIN) of the drivingcurrent I_(DRV) are represented by the following Expressions.

I _(MAX) =ΔI/1023×(1023−(Y×4))

I _(MIN) =ΔI/1023×(−Y×4)

The above is the operation of the driving circuit 2.

With the driving circuit 2, such an arrangement is capable of settingthe ratio between the negative driving current I_(MIN) and the positivedriving current I_(MAX) to a desired value. This allows a common driving2 circuit to drive various kinds of VCMs 200. Also, such an arrangementallows various kinds of platforms to employ such a common drivingcircuit 2 to drive the VCM 200.

The driving circuit 2 is capable of setting the minimum driving currentI_(MIN) to 0 mA, or otherwise of setting the maximum driving currentI_(MAX) to 0 mA. That is to say, such an arrangement is capable ofgenerating the driving current I_(DRV) in only one direction. Thus, thedriving circuit 2 can be employed as a driving circuit for the springreturn method. That is to say, by employing such a common drivingcircuit 2, such an arrangement allows the user to operate a givenplatform regardless of whether the platform employs a bi-directionaldriving method or a spring return method. Such an arrangement providesreduced design time.

Next, description will be made regarding a specific example of anelectronic device 500. FIG. 4 is a perspective view showing a cellularphone terminal which is an example of the electronic device 500. Theelectronic device 500 includes a housing 501, a lens module 502, and animage acquisition element 504. The image acquisition element 504 isbuilt into the housing 501. The housing 501 is provided with an openingat a position at which it overlaps the image acquisition element 504.The lens module 502 is provided to the opening.

With the aforementioned driving circuit 2, changing the referencevoltage V_(REF) is equivalent to superimposing, on the detection voltageV_(S), a shift voltage that can be set by means of an external circuit.Furthermore, the same effect can be provided by superimposing, on thecontrol voltage V_(CNT) instead of the detection voltage V_(S), a shiftvoltage that can be set by means of an external circuit. By extendingthis idea, the following technical idea can be derived.

That is to say, the driving circuit 2 may be configured to be capable ofsuperimposing a shift voltage, which can be set by means of an externalcircuit, on at least one from among the control voltage V_(CNT) and thedetection voltage V_(S). Furthermore, the error amplifier 20 maypreferably generate the error voltage V_(ERR) such that the controlvoltage V_(CNT) is equal to the detection voltage V_(S) after a shiftvoltage is superimposed on at least one from among the control voltageV_(CNT) and the detection voltage V_(S).

Thus, by adjusting the value of the shift voltage, such an arrangementis capable of freely setting the range in which the driving currentI_(DRV) can be set according to the control voltage V_(CNT). Thistechnical idea includes the following specific embodiments.

1. A shift voltage that can be set according to correction data receivedfrom an external circuit is superimposed on (is added to or otherwisesubtracted from) the detection voltage V_(S). This embodiment includesthe following techniques.

1.1 The reference voltage V_(REF) is configured as a variable voltage.This technique has been described in the embodiment.

1.2 An analog adder/subtractor unit is provided as an upstream stage ofthe error amplifier 20, so as to add the shift voltage that correspondsto the correction data D_(REF) to, or otherwise to subtract the shiftvoltage from, the detection voltage V_(S). Furthermore, the outputvoltage of the analog adder/subtractor unit is output to the erroramplifier 20.

2. A shift voltage that can be set according to correction data receivedfrom an external circuit is superimposed on (is added to or otherwisesubtracted from) the control voltage V_(CNT). This embodiment includesthe following techniques.

2.1 An analog adder/subtractor unit is arranged between the erroramplifier 20 and the first D/A converter 52 so as to add a shift voltagethat corresponds to the correction data D_(REF) to, or otherwise tosubtract the shift voltage from, the control voltage V_(CNT).Furthermore, the output voltage of the analog adder/subtractor unit isoutput to the error amplifier 20.

2.2 Digital calculation is performed on the control data D_(CNT) and thecorrection data D_(REF), each configured as digital data, so as togenerate a digital value. The digital value thus obtained is D/Aconverted by means of the first D/A converter 52 into an analog value.The analog value thus converted is supplied to the error amplifier 20.

3. The input offset voltage of the error amplifier 20 (secondoperational amplifier 22) is configured as a variable voltage.Furthermore, the offset voltage of the error amplifier 20 is adjustedaccording to the correction data received from an external processor.

Description has been made regarding the present invention with referenceto the embodiments. The above-described embodiments have been describedfor exemplary purposes only, and are by no means intended to beinterpreted restrictively. Rather, it can be readily conceived by thoseskilled in this art that various modifications may be made by makingvarious combinations of the aforementioned components or processes,which are also encompassed in the technical scope of the presentinvention. Description will be made below regarding such modifications.

Modification 1

Description has been made in the embodiment regarding an arrangement inwhich the first driver 30 and the second driver 40 provide lineardriving of the VCM 200. However, the VCM 200 may be PWM driven. That isto say, the first driver 30 and the second driver 40 may generate pulsedriving voltages V_(O+) and V_(O−), respectively. Furthermore, the firstdriver 30 and the second driver 40 may adjust the duty ratios of thedriving voltages V_(O+) and V_(O−), respectively, according to the errorvoltage V_(ERR).

Modification 2

Description has been made in the embodiment regarding an arrangement inwhich the detection resistor R_(NF) is arranged between the seconddriver 40 (first driver 30) and the coil L1. However, the position ofthe detection resistor R_(NF) is not restricted to such a position. Thedetection resistor R_(NF) may be arranged in series with the high-sidetransistor MH between the output terminal OUT+(OUT−) and the powersupply line. Also, the detection resistor R_(NF) may be arranged inseries with the low-side transistor ML between the output terminal OUT+(OUT−) and the ground line. Also, the on resistances of the transistors(MH, ML) that form an output stage of the first driver 30 and/or the onresistances of the transistors (MH, ML) that form an output stage of thesecond driver 40 may be used as the detection resistor R_(NF).

Also, in a case in which the DC resistance component (parasiticresistance) of the VCM 200 is a known value, the DC resistance componentmay be used as the detection resistor R_(NF). The voltage across bothends of the VCM 200 is represented by the sum of the voltage drop thatoccurs at the resistance component and the back electromotive force thatoccurs across the inductance L1. Thus, the current detection circuit 10may eliminate the back electromotive force that occurs at the coil L1from the voltage across both ends of the VCM 200, so as to detect thevoltage drop that occurs at the resistance component. Such a currentdetection circuit may be configured using known techniques.

Modification 3

Description has been made in the embodiment regarding an arrangement inwhich the CPU 508 supplies the digital control data D_(CNT) and thedigital reference data D_(REF). However, the present invention is notrestricted to such an arrangement. For example, at least one pin isprovided to the driving circuit 2 in order to allow the referencevoltage V_(REF) to be set. Specifically, the reference voltage V_(REF)may be set according to a combination of pins (which indicateshigh-level voltage, low-level voltage, or otherwise high impedance).Also, the driving circuit 2 may receive, from an external circuit, thereference voltage V_(REF) configured as an analog signal.

Modification 4

Description has been made in the embodiment regarding a lens module forfocusing. However, the usage of the driving circuit 2 is not restrictedto such an application. For example, the VCM 200 may drive a lensemployed for image stabilization.

While the preferred embodiments of the present invention have beendescribed using specific terms, such description is for illustrativepurposes only, and it is to be understood that changes and variationsmay be made without departing from the spirit or scope of the appendedclaims.

What is claimed is:
 1. A driving circuit that supplies a bi-directionaldriving current to a voice coil motor, the driving circuit comprising: acurrent detection circuit that generates a detection voltage V_(S)represented by V_(S)=V_(REF)+k×I_(DRV), with the driving current asI_(DRV), with a reference voltage as V_(REF), and with a gain as k; anerror amplifier that amplifies a difference between the detectionvoltage V_(S) and a control voltage that indicates a position of thevoice coil motor so as to generate an error voltage; a first driver thatis connected to one end of a coil of the voice coil motor, and thatswitches the driving current between a state in which the drivingcurrent flows as a source current and a state in which the drivingcurrent flows as a sink current according to the error voltage; and asecond driver that is connected to the other end of the coil of thevoice coil motor, and that switches the driving current between a statein which the driving current flows as a sink current and a state inwhich the driving current flows as a source current according to theerror voltage, wherein a level of the reference voltage V_(REF) issettable externally.
 2. The driving circuit according to claim 1,wherein the current detection circuit comprises: a detection resistorarranged on a path of the driving current; a first operationalamplifier; a first resistor arranged between a first input terminal ofthe first operational amplifier and a first end of the detectionresistor; a second resistor arranged between a second input terminal ofthe first operational amplifier and a second end of the detectionresistor; a third resistor arranged between an output terminal of thefirst operational amplifier and the first input terminal of the firstoperational amplifier; and a fourth resistor having one end connected tothe second input terminal of the first operational amplifier and anotherend to which the reference voltage is applied.
 3. The driving circuitaccording to claim 1, further comprising: a first D/A converter thatconverts, into the control voltage configured as an analog signal,digital control data that is received from an external processor andthat indicates the position; and a second D/A converter that converts,into the reference voltage configured as an analog signal, correctiondata that is received from the external processor and that indicates thereference voltage.
 4. The driving circuit according to claim 2, whereinthe detection resistor is arranged between the first end of the coil andan output terminal of the first driver, or otherwise between the secondend of the coil and an output terminal of the second driver.
 5. Thedriving circuit according to claim 2, wherein an on resistance of atransistor that forms an output stage of the first driver and an onresistance of a transistor that forms an output stage of the seconddriver are used as the detection resistor.
 6. The driving circuitaccording to claim 2, wherein a known DC resistance component of thevoice coil motor is used as the detection resistor.
 7. The drivingcircuit according to claim 1, wherein the error amplifier comprises: asecond operational amplifier having a first input terminal to which thecontrol voltage is input; a first capacitor arranged between a secondinput terminal and an output terminal of the second operationalamplifier; and a fifth resistor having a first end connected to thesecond input terminal of the second operational amplifier and a secondend to which the detection voltage V_(S) is applied.
 8. The drivingcircuit according to claim 1, wherein the first driver comprises anon-inverting amplifier that amplifies the error voltage with apredetermined common voltage as a reference voltage so as to apply afirst driving voltage to the one end of the coil, and wherein the seconddriver comprises an inverting amplifier that amplifies the error voltagewith the common voltage as a reference voltage so as to apply a seconddriving voltage to the other end of the coil.
 9. The driving circuitaccording to claim 1, wherein the first driver comprises: a firstvoltage-dividing circuit that divides, with a predetermined voltagedivision ratio, a voltage difference between a first output voltage thatdevelops at the one end of the coil and a predetermined common voltage;and a first amplifier that comprises a first push-pull output stageincluding a high-side transistor and a low-side transistor, and thatcontrols the high-side transistor and the low-side transistor of thepush-pull output stage such that the voltage obtained by voltagedivision by means of the first voltage-dividing circuit approaches tothe error voltage, and wherein the second driver comprises: a secondvoltage-dividing circuit that divides, with a predetermined voltagedivision ratio, a voltage difference between a second output voltagethat develops at the other end of the coil and the error voltage; and asecond amplifier that comprises a second push-pull output stageincluding a high-side transistor and a low-side transistor, and thatcontrols the high-side transistor and the low-side transistor of thepush-pull output stage such that the voltage obtained by voltagedivision by means of the second voltage-dividing circuit approaches tothe common voltage.
 10. A driving circuit that supplies a bi-directionaldriving current to a voice coil motor, the driving circuit comprising: acurrent detection circuit that generates a detection voltage V_(S) thatcorresponds to the driving current; an error amplifier that amplifies adifference between the detection voltage V_(S) and a control voltagethat indicates a position of the voice coil motor so as to generate anerror voltage; a first driver that is connected to one end of a coil ofthe voice coil motor, and that switches the driving current between astate in which the driving current flows as a source current and a statein which the driving current flows as a sink current according to theerror voltage; and a second driver that is connected to the other end ofthe coil of the voice coil motor, and that switches the driving currentbetween a state in which the driving current flows as a sink current anda state in which the driving current flows as a source current accordingto the error voltage, wherein the driving circuit is capable ofsuperimposing a shift voltage that is settable by means of an externalcircuit on at least one of the control voltage and the detection voltageV_(S), and wherein the error amplifier generates the error voltage suchthat the control voltage approaches to the detection voltage after theshift voltage is superimposed on at least one of the control voltage andthe detection voltage.
 11. The driving circuit according to claim 10,wherein the current detection circuit generates a detection voltageV_(S) represented by V_(S)=V_(REF)+k×I_(DRV), with the driving currentas I_(DRV), with a reference voltage as V_(REF), and with a gain as k,and wherein the level of the reference voltage V_(REF) is settableaccording to correction data received from an external processor. 12.The driving circuit according to claim 10, wherein the control voltageis obtained by adding a shift voltage that corresponds to correctiondata received from an external processor to a voltage that correspondsto digital control data that indicates a position of the voice coilmotor received from the external processor.
 13. The driving circuitaccording to claim 10, wherein the control voltage is obtained as avoltage by adding correction data received from an external processorto, or otherwise by subtracting the aforementioned correction data from,digital control data that indicates a position of the voice coil motorreceived from the external processor, and by converting the digitalvalue thus obtained into an analog voltage.
 14. The driving circuitaccording to claim 10, further comprising an adder that is arranged asan upstream stage of the error amplifier, and that adds a shift voltagethat corresponds to correction data received from an external processorto, or otherwise subtracts the aforementioned correction data from, thedetection voltage.
 15. The driving circuit according to claim 10,wherein an offset voltage of the error amplifier is adjustable accordingto correction data received from an external processor.
 16. The drivingcircuit according to claim 1, monolithically integrated on a singlesemiconductor substrate.
 17. A lens module comprising: a focusing lens;a voice coil motor arranged such that a moving element thereof iscoupled with the focusing lens; and the driving circuit according toclaim 1, that drives the voice coil motor.
 18. A lens module comprising:an image stabilization lens; a voice coil motor arranged such that amoving element thereof is coupled with the image stabilization lens; andthe driving circuit according to claim 1, that drives the voice coilmotor.
 19. An electronic device comprising: the lens module according toclaim 17; and an image acquisition element that acquires an image basedon light that has passed through the lens module.
 20. An electronicdevice comprising: the lens module according to claim 18; and an imageacquisition element that acquires an image based on light that haspassed through the lens module.